Electronic relay



Dec 6, 1949 .J. NIGRO ELECTRONIC RELAY Filed March 30, 1945 E m w m A T TORNEYS.

Patented Dec. 6, 1949 UNITED STATES PATENT OFFICE ELECTRONIC RELAY John Nigro, Florham Park, N. J. n ne n iv arc 30, 1945, s i l no. 535,

. Claims. (01. 179-471) This invention pertains to an electronic relay or amplifier circuit for alternating currents, haying discriminatory and variable amplification characteristics such that input signals below any desired preselected level may be substantially suppressed, while those above said level'may be amplified to a progressively increasing degree with increasing input signalstrength. The arnplifier of the invention is adjustable with respect to both of the above features, so that either may be varied or eliminated if desired for any particular operation.

The invention is of especial utility as an audiofrequency amplifier in radio broadcast receivers or in phonograph pick-up and amplifying systems, by reason of its suppression of background noise, needle scratch, static and the like','-combined with its restoration of the reproduced sound eifects to a fidelity of response and volume in tensity variation commensurate with the original sound efiects produced in the broadcasting or recording studios.

In connection with the latter, the audio-amplification circuits heretofore employed in commercial broadcasting and recording studios, have usu ally been such" as to compress the" amplitude variations of the" output signals within a relatively narrow range as compared to the intensity variations of the original sound effects. This has been particularly true as applied tosystems employing frequency modulatiornthe amplitude variations of which, in order to avoid serious fre' quency distortion, must be confined within relatively narrow limits, for example, within five percent of the carrier'strength. Consequently when such programs are reproduced,'r'elatively sligh't diiferences in volume are'observed at the'receiver or phonograph loud speaken'as between'the high amplitude and low amplitude signals. Furthermore, insofar as I am aware, no completely satisfactory solution has been proposed with respect to the problem of'eliminating background noise, static, needle scr'atch,etc'.

The present invention provides an amplifier adapted to correct the above mentioned defects, by employment of a pentode tube, to the screen and suppressor grids of which, negative and positive biasing potentials are respectively applied, of such magnitudes as to suppress signals below a preselected amplitude impressed on the control grid, while amplifying stronger signals. By virtue of this feature, the low-level background noises, static and needle scratch effects, tc., are eliminated, while the desired higher level sound producing signals are amplified and transmitted to the amplifier output.

In order to provide increasedamplification with increasing signal strength, above the suppression level, a portion of the amplified output of the pentode tube, is rectified and applied in a positive sense as an additional biasing potential to the screen grid, supplementing the above mentioned negative bias, and such that the resultant bias on the screen grid is the algebraic sum of these two. Accordingly as the signal strength applied to the control grid increases above the suppression level, the screen grid will become decreasingly negative or increasingly positive, whereby the amplification factor of the pentode is progressively increased. In this way the higher amplitude input signals are amplified to a greater extent than low amplitude signals. By appropriately adjusting the negative bias and the rectifled portion of the amplifier output applied as a positive bias to the screen grid, the amplification factor may be caused to increase at any desired rate with increasing signal strength, and such that the amplified output can be made to simulate closely the intensity variations of the original sound effects as produced in the broadcasting or recording studios.

The invention is also applicable as a highly sensitive electronic relay for electrically actuating such devices as burglar alarms, display signs, toys, etc., as explained below.

"The 'singlefigure of the drawing shows diagrammatically a preferred circuit arrangement according to the invention.

' Referring to the drawing, the amplifier of the invention includes a variable mu pentode tube I, operating as an amplifier stage, the pentode being provided with the customary, indirectly heated cathode 2, control grid 3, screen grid 4, suppressor grid 5, and anode 6. The cathode 2 may be directly grounded as shown at I, or may, byoperation' of switch 8, be grounded through a plate'current biasing resistor shunted by a bypass condenser, as indicated at 9.

Signals to be amplified are impressed on input terminals ll, between which is connected, the fixed arm of a potentiometer l2, grounded at one end as shown, and the variable arm of which is connected to the control grid 3. This variable potentiometer operates as a master or maximum setting control of the amplifier circuit.

The cathode 2 is indirectly heated in the conventional manner (not shown for simplicity). The plate circuit of the pentode is energized by a source'of B voltage, such as that derived from a power pack, so connected between terminals l3, that the upper terminal is plus and the lower terminal minus, as indicated. From the B terminal, a connection Ht extends through an adjustable resistor l5 to ground for purposes presently to be explained. The +B terminal is connected to the pentode plate 6 over a conductor i6 and through an alternating current blockingfilter circuit, comprising series resistors ll, Na and grounded shunt condenser [8.

The alternating current output of the pentode is fed from the plate 6, over a branch circuit l9 to the input of one or more additional amplifier 3 stages 20, of conventional design, the output of which is applied through a transformer 2|, to a translating device 22, for example a loud speaker, relay or the like, as referred to hereinafter.

For causing the pentode to respond only to signals above a preselected level, a negative biasing potential of appropriate value is applied to the screen grid 4 thereof, while a positive biasing potential of suitable magnitude is applied to suppressor grid 5. The negative biasing potential for the screen grid, is derived from the -B voltage drop to ground across resistor 15, the upper terminal of which is connected through a filter resistor 23, the variable portion of a potentiometer 24, and through a filter resistor to the screen grid 4. In the circuit above described, condensers 26, 21 serve to by-pass or filter off alternating current components. The negative biasing potential thus applied to the screen grid may be varied by adjusting resistor [5, but once suitably determined, is normally left undisturbed as a fixed bias.

The positive biasing potential applied to the suppressor grid 5, is derived from the +3 voltage at terminal l3, applied through the serially connected fixed resistors 28, 29, and variable resistor 3| to ground at 32. This circuit constitutes a potentiometer to which the suppressor grid 5 is tapped between resistors 29 and 3D. Alternating current components are filtered 01f to ground through the by-pass condensers 33, 34. The positive potential thus applied to the suppressor variable resistor 3|, but once suitably adjusted is left undisturbed as a fixed positive bias on the suppressor grid.

Variable resistor 3| functions as the minimum setting control for the circuit in determining the level below which signals are suppressed.

In order to provide an amplification factor for the system which increases progressively with the input signal amplitude above the suppression level, a portion of the amplified output impressed on the secondary winding of transformer 2|, is rectified and applied as a positive bias to the screen grid 4. To this end a connection 36 extends from the upper terminal of the transformer secondary to the anodes 31 of a rectifier 38, here shown as a duo-diode tube although any suitable rectifier may be employed. The lower terminal of transformer winding 35, is connected over a conductor 39 through the fixed arm of potentiometer 24, and a filter resistor to the cathodes 4! of the rectifier 38. Condensers 42, 43 are filter condensers for the circuit above described.

The complete rectifier circuit is thus traced from the lower terminal of secondary winding 35, over conductor 39, through potentiometer 24, resistor 40, and rectifier 3B, returning over conductor 36 to the upper terminal of secondary winding 35.

A rectified component of the amplified output thus flows through the fixed arm of potentiometer 24, the variable arm of which is tapped through resistor 25 to the screen grid 4 of the pentode. This rectified current fiows through potentiometer 24 in such direction as to apply a positive biasing potential to the screen grid 4, which supplements the negative bias applied thereto by the --B voltage drop across resistor I5, and such that the resulting bias applied to the screen grid is the algebraic sum of these two biasing voltages. Since the negative bias remains relatively fixed, while the positive bias increases with the signal strength impressed upon the input terminals I I, the resulting bias on the grid, may be varied by adjustment of 4 screen grid 4, increases, in a positive direction, with increase in input signal strength. Hence, as the signal increases in strength above the suppression level, the bias on the screen grid becomes decreasingly negative, passing through zero to a positive value for exceedingly strong input signals. This has the effect of progressively increasing the amplification factor of the system with increasing signal strength above suppression level, and for purposes above explained.

The rate at which the amplification factor is thus increased with signal strength, is determined by the adjustment of the variable arm of potentiometer 24. As this variable arm is moved downwardly in the drawing, the rate of increase of the amplification factor is decreased, and conversely if the variable arm is shifted upwardly in the drawing.

At the output end of the system the translating device 22 may be a loud speaker, in case the system is being employed to reproduce sound effects of radio broadcast programs or phonograph pick-up. On the other hand, if the system is desired for use as a burglar alarm, or for actuation of display signs, toys and the like, the translating device would be a suitable relay for such purposes.

The overall operation of the system as above described may be further elucidated as follows: The circuit including resistor l5 for applying the negative biasing potential to the screen grid 4, prevents signals below the desired level impressed on the input terminals [2, from being amplified.

; the suppressor grid by the circuit above explained including variable resistor 3|. Adjustment of this resistance 3 I, varies the positive biasing voltage applied to the suppressor grid, and thereby varies the flow of cathode current to the plate 4 electrode 6; and also concurrently compensates by Vernier-like adjustment for the setting of variable resistor [5 in the screen grid circuit. The result is that input signals below the preselected level, are suppressed, while stronger signals are amplified.

Suitable values for the various circuit components of the amplifier, when constructed for audio-frequency operation, are as follows:

Resistor 9:3,000 ohms Condenser=10 mfds. Potentiometer l2=1 megohm Resistor I5=50 ohms Resistor l1=50,000 ohms Resistor lla=150,000 ohms Condenser l8=8 mfds.

Resistor 23=50,000 ohms Potentiometer 24=250,000 ohms Resistor 25:0.5 megohm Condenser 26:0.25 mfd. Condenser 21:0.1 mfd.

Resistor 28=50,000 ohms Resistor 29=250,000 ohms Resistor 30=100,000 ohms Resistor 3|=0.5 megohm Condensers 33 and 34:0.25 mfd. each Resistor 40=50,000 ohms Condensers 42 and 43:0.1 mfd. each What is claimed is:

1. An electronic amplifier for alternating current signals, comprising: a pentode tube having control grid, screen grid, suppressor grid, cathode and anode electrodes; input and output circuit-s connected to said control grid and anode respectively; and means independent of said control grid and input circuit for applying a negative biasing potential to said screen grid and a positive biasing potential to said suppressor grid such that input signals below a preselected level are suppressed, and above said level are amplified.

2. An electronic relay, comprising: a pentode tube having control grid, screen grid, suppressor grid, cathode and anode electrodes; input and output circuits connected to said control grid and anode respectively; means for applying a negative biasing potential to said screen grid and a positive biasing potential to said suppressor grid, such that input signals below a preselected level are suppressed and above said level are amplified; and means for applying to said screen grid, a supplemental positive biasing potential derived from said amplified signals, thereby to vary the amplification factor of said relay in a preselected manner with variation in signal strength impressed on said input circuit.

3. An electronic relay, comprising: a pentode tube having control grid, screen grid, suppressor grid, cathode and anode electrodes; input and output circuits connected to said control grid and REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 20,422 Pfister July 14, 1934 2,219,729 Tahon Oct. 29, 1940 2,230,243 Haffcke Feb. 4, 1941 2,250,559 Weber July 29, 1941 2,305,543 McCarty Dec. 15, 1942 2,305,873 Holst Dec. 22, 1942 OTHER REFERENCES Reich, Theory and Applications of Electron Tubes, published 1939, by McGraw-Hill Book 00., N. Y., page 58. (Copy in Div. 69.) 

